Sockington (Jason Scott) has 1,476,142 followers

Who he is: Sockington is Jason Scott's cat. Scott is a computer historian in Waltham, MA who's cat Sockington was up always up to no good. Scott decided to make a Twitter account for Sockington's "thoughts," and his feed became increasingly popular.

Stefanie Michaels has 1,492,318 followers

Who she is: Stefanie Michaels, known to many as Adventure Girl, started out as a model for upscale swimwear companies who eventually launched her own promotional business SMC Productions. Her business took her around the country and she started a website with a journal of her travels. Her popularity grew as a travel expert and she now has a book, her own website, and was named "America's Tweetheart," by Vanity Fair in February 2010.

Heather Armstrong has 1,564,866 followers

Who she is: Heather Armstrong launched dooce.com in 2001 to talk about pop culture and her life as a single woman in LA. After being fired from her full time job because she wrote about it on dooce.com, her website became her focus. Armstrong and her husband now run enough ads on their website to support her family. She blogs about being a wife and mother of two.

Why people follow her: People can relate to her tweets.

Typical tweet: When I ask someone how they're doing and they start to give an honest answer, I immediately fall to the ground and fake a groin injury.

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Jack Dorsey has 1,718,769 followers

Who he is: Jack Dorsey is one of the co-founders of Twitter, and current chairman. His most recent startup is Square, a mobile payment system which allows people to accept credit card payments on the iPhone.

Why people follow him: One of the greatest tech entrepreneurs alive; also hobnobs with celebrities and tweets about it.

Biz Stone has 1,764,057 followers

Who he is: Biz Stone is one of the co-founders of Twitter. Stone has published two books on social media and has a blog, and he's now working on an incubator called Obvious with fellow Twitter co-founder Evan Williams.

Why people follow him: An expert source of social media news.

Typical tweet: "Truth passes through three stages: First, it is ridiculed; Second, it is violently opposed; Third, it is accepted as being self-evident."

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Justin Halpern has 2,628,049 followers

Who he is: Justin Halpern is a 29-year-old who lives with his 74-year-old retired dad. Halpern started his Twitter page dedicated to ridiculous things his father said throughout the day. His Twitter has now inspired a book entitled Sh*t My Dad Says and the television series $#*! My Dad Says on CBS.

Why people follow him: Extremely funny.

Typical tweet: "I didn't say you were ugly. I said your girlfriend is better looking than you, and standing next to her, you look ugly."